Re: why is my roast beef iridescent?

I recall that a colleague of mine (Dr. LaBudde) posted a nice answer on a 
food safety discussion list a few years back.

The link to the archived message is: 
http://listserv.nal.usda.gov/cgi-bin/wa?A2=ind9804&L=foodsafe&F=&S=&P=25842


But the full text of his reply is:

"The iridescence on the surface of cut meats (usually those which are
processed with the addition of water and phosphates) is due to the surface
moisture content and index of refraction increase from dissolved solids.
Phosphates in particular greatly increase the effect. 

"Dry surfaces scatter and absorb rather than reflecting and refracting
light. So the effect is normally only seen in meat which has been processed
to increase moisture content or which is exudative.

"The iridenscent sheen is seen typically in ham, corned beef and smoked
turkey. Since fat is translucent, it tends to nullify the effect by
scattering and absorption. Consequently the effect is not noticeable in
such products as bologna, etc.

"The effect is purely optical and is harmless. You may take it as an
indicator of high leanness (low fat content) of the meat involved."